In such a known device for controlling a swingable spool holder (see German Pat. No. 29 31 344), there is provided as a pneumatic drive device a bellows which can be expanded with compressed air. If a thread breakage occurs, then the feeler lever swings and moves the control valve into its second switching position. Through this, the compressed-air line is directly connected to the compressed-air source and compressed air flows into and expands the bellows, so that it lifts the spool holder. Through this, the spool is lifted from the friction roller. Since the friction roller no longer drives the spool, the spool stops rotating. Particularly in the case of a slow winding speed, the end of the broken thread is not completely wound up onto the spool before the spool stops rotating. Moreover, the loose thread end is sometimes caught by the rotating friction roller and wound onto the friction roller, causing thread to be unwound from the spool and wound onto the friction roller. Aside from the loss of thread which occurs through this and the necessity of removing the thread manually from the friction roller, this also often leads to machine damage and thus to expensive idle time.
In another conventional pneumatic device for swinging the spool holder (see German Offenlegungsschrift No. 23 51 311), the pneumatic drive device has a piston which is movable in a cylinder and, when biased by compressed air, can be connected by a clamping device to an operating rod which is in turn pivotally connected to the spool holder. The clamping device is arranged on an intermediate member, relative to which the piston is initially axially freely movable, the piston thereafter engaging the intermediate member and carrying it along. With this device, it is supposed to be achieved that the spool holder, for any diameter spool, is always lifted by the same amount. This amount corresponds with the amount of movement of the intermediate member, which can be varied by adjustable stops. In this known device, the piston moves for a certain axial distance before it moves the operating rod. Since, however, the piston is biased with the full pressure of the compressed-air line, the time period from the application of pressure to the point in time at which the piston moves the operating rod is very short. This short time period is not sufficient to ensure a complete winding up of the loose thread end on the spool.
A basic purpose of the invention is therefore to provide a drive for a swingable spool holder of the abovementioned type, in which a delay of the lifting of the spool from the friction roller is provided to ensure a complete winding up of the loose thread end onto the spool before the spool stops rotating.